You say the inside door handles don't work, or work intermittently. This indicates a mechanical issue within the latch mechanism. Since you are reporting from the Nation's Ice Box, I'm sure this is your problem. Since you can pull the door latches and clean them for free, you should do this before spending your hard-earned cash on a GM5.

GM5 can control whether or not your interior handles work. Lock your car with the key and try using the interior handles.